1. Field of the Invention
The preset invention relates to a method of sharing resources between devices using wireless connectivity, and in particular to the sharing of a radio link to a remote base station or access point between several devices located within a small geographical area.
2. Description of the Related Art
A mobile phone network comprises a series of base stations covering a range of geographical areas, and a multiple of handsets. Each handset communicates with one of the base stations, and the particular base station used is selected depending on factors such as geographical location, interference, channel loading, etc.
However, an increasing problem with this arrangement is that the number of people using mobile phones is increasing rapidly, and there is only a limited amount of bandwidth available for transmission of signals to and from individual handsets. Radio links from laptop computers, personal organisers, etc., are also becoming much more common, for example, to connect to the internet (e.g. WAP), for fax, video conferencing, telematics, or for remote control of hardware devices such as domestic appliances in the home.
The traditional approach to this problem of limited bandwidth has been to introduce more and more complex methods of scheduling. Air interface modes such as TDMA (time-division multiple access), e.g. GSM (Global System for Mobile communications, are based on dividing time into slots and placing the signals of different users into different time slots. Another way of using the available bandwidth, which may be more efficient, is CDMA (code division multiple access), in which signals from multiple users are sent at the same time in the same frequency band, with the spectrum of each user's signal spread through the bandwidth of the frequency band according to a code sequence unique to the user. One of the most important implementation of CDMA is W-CDMA (wideband CDMA), which uses a 5 Mhz carrier, allowing the possibility of multimedia transmission such as video streams.
In the earlier implementation of CDMA, blind interfrequency handover could result in inadequate call quality. Instead, a mobile radio had to be able to monitor the signal strength and and quality of another carrier frequency while still maintaining the connection in the current carrier frequency. In the case of W-CDMA, this need can be overcome by having the system enter compressed mode to simultaneously monitor other carriers. In compressed mode, the system is manipulated to provide a number of contiguous slots free for measuring other channels. However, compressed mode requires a highly complex level of network management. A variety of methods can be used to establish compressed mode, for example through reduced spreading factor (perhaps with increased transmit power), increased puncturing, or higher layer signalling. In each case, the mobile terminal will suffer as the raw throughput of the channel is being reduced. In the case of reduced spreading factor, the receiver may experience greater interference (and create greater interference, if a higher base station transmit power is used). With puncturing, the error detection/correction properties of any coding may be impaired. Finally, with higher layer signalling, certain segments of data must be scheduled to not be transmitted which may degrade overall perceived quality.
In general, a mobile device may have to spend a significant amount of time monitoring: other carriers, base stations; access points within the same radio mode; or carriers, base stations or access points which are attached to another mode. This monitoring time may impact on the throughput (as observed by the user), power consumption, and the latency which is introduced before a handover to an alternative carrier, base station, access point, or mode.
In addition to the user of more complex air interface modes, wireless devices themselves are becoming increasingly complex, as a larger and larger set of radio functionality and applications are required. The trend has been towards integrating all the required technology in a single device, to allow the user flexibility of operation. This desire of highly complex functionality, flexibility and multiple air interface modes leads towards the “Software Defined Radio” concept where a flexible architecture is employed to fulfil all requirements.
In recent times it has also become feasible to provide an independent low power interconnection between devices through the use of a Wireless Personal Area Network (WPAN), such as a Bluetooth enabled WPAN. Within WPAN equipped devices, this mode of operation is likely to exist in addition to (and independently of) other capabilities, such as: cellular or Wireless Local Area Network (WLAN) transceivers; significant processing power; and other features. The provision of this independent link gives the potential for a device to utilise the resources of other devices that are attached with the wireless interconnection. This concept of a virtual device that is formed from a number of separate wireless units is described here as a distributed wireless system of distributed radio.
The separate wireless units are likely to be manufactured independently and even independently owned, but are linked through a preferably common short-range wireless link with a common communications protocol. It would also be possible to use more than one type of link within the WPAN, although there may then be more problems with the upper layers in terms of forwarding information over multiple link types.
A further problem with mobile radio device is that they tend to be battery operated, but the radio links to the base station must be of reasonably high power. This is a major factor in draining the batteries, and reducing the amount of time before recharging is necessary.